I have a '91 L03/T5 bird and I have a 160 stat, 177/166 fan switch. My gas mileage is ~17mpg for mixed driving. I plan on either getting a chip or programming myself to get the car into closed loop earlier and I'm hoping that will get my gas mileage up some.
Does anyone know if this will get my mileage back up closer to stock? or should I just go with a 180 deg setup with stock tuning? If anyone has either 180 setup w stock tuning or 160 tuned can you post your mpg so I can see what kind of difference itll make.

 

Before I rebuild my top end on my 1990 LO3/auto, I was getting close to 30mpg highway stock - you may just need a good tuning - I'd think you could get better with a 5sp. than I did on an auto.

 

Wow 30mpg...I definately need a tune or to go up in temp then.

 

Dith the 160° stat. You can leave the fan switch but you shouldn't run lower than a 180° stat. Unless you are in a super warm climate a 160° stat will delay closed loop operation and in some caes (depending on ambient temperature) may not ever get there. If you want to go into closed loop sooner than you you need to have the right parts that don't keep your motor constantly cool. I would run a normal thermostat and keep the fan switch. That way your car will close to its desired static temperature of 195°. The fan switch will just kick the fans on sooner when you exceed 195°.

 

Yeah I decided to go with a 180 stat. I ordered a new fan switch because I don't want my fan to be continually running if the turn on time is 176 and turn off is 166 I figured it would always run cuz the stat wouldnt start opening till 180.

 

I don't think you have a problem with the temp of the motor, you probably need a new O2 sensor and some plugs, wires, cap/rotor.

My 89 with 203,000 miles gets about 26-27 mpg on the highway with 3.08 gears and T-5 and I run a 160 t-stat with stock fan on temps around 220 degrees. Going down the freeway in about 60 degree weather the car runs around 175 degrees.

 

Yeah, that prob was part of it 89GTA. I just changed the cap rotor plugs and wires today and it drives a lot smoother, the plugs looked really old and the rotor and top of distrubuter where rusted and corroded so I wire brushed everything and put a good amount of dielectirical grease so hopefully now that should help with the mileage.

BTW why do you use a 160 stat and stock fan setting?? that'll make your car fluctuate between 160s and 220s. Seem like keeping the stock fan switch would defeat the purpose of the 160 stat cuz usually the cars run hot in traffic not on highway and that's all the stat would help with i thought.

 

The 160 stat was in it when I bought it and really has no effect on anything besides warm-up time and running a little cooler on the freeway. Besides that, it runs like stock. This car is my daily driver, so performance takes a back seat to mods.

 

It may run normal but the ECM will read CTS values and sense a "cool" condition and use more fuel to compensate.